The present invention relates to communications apparatus such as a mobile telephone set to perform mobile communications, a frequency control method for communications apparatus, and a recording medium on which a program to execute the frequency control method is recorded, and in particular, to communications apparatus, a frequency control method for communications apparatus, and a recording medium which allow frequency offset correction without degradation in the accuracy of the sending or sending/receiving reference frequency and demodulation characteristics, despite degradation in the accuracy caused by nonlinearity, temperature characteristics and secular change of a voltage-controlled oscillator or reference oscillator.
FIG. 4 is a block diagram of related communications apparatus equipped with a frequency offset correction feature (hereinafter referred to as a first related art).
In FIG. 4, communications apparatus according to the first related art comprises antennas 401 and 411, mixers 402 and 412, local oscillators 403 and 413, voltage-controlled oscillators 404, an A/D converter 405, D/A converters 406 and 415, demodulating means 407, receiving frequency offset estimating means 408, modulating means 417 and a central processing unit (CPU) 421.
According to communications apparatus of the first conventional related art, reception signals received via the antenna 401 are frequency-converted via the mixer 402, and a frequency offset estimate FOS is determined via the receiving frequency offset estimating means 408. Reference frequency control, so-called the AFC (Auto Frequency Control) is made by using the CPU 421 to feedback a control value based on the determined frequency offset estimate FOS to the voltage-controlled oscillator 404 via the D/A converter 406.
While the demodulating means 407 demodulates intermediate-frequency signals frequency-converted by the mixer 402 and outputs upstream control data DTD and downstream control data DCD to the CPU 421, the CPU 421 can control the sending reference frequency by using the downstream control data DCD from the demodulating means 407, besides the AFC processing. In this case, a frequency offset control value is generated by the CPU 421 based on a sending reference frequency command on the downstream control data DCD, and fed back to the voltage-controlled oscillator 404 via the D/A converter 406.
FIG. 5 is a block diagram of another conventional communications apparatus equipped with the frequency offset correction feature (hereinafter referred to as a second related art).
In FIG. 5, communications apparatus according to the second related art comprises antennas 401 and 411, mixers 402 and 412, local oscillators 403 and 413, a reference oscillators 404, an A/D converter 405, D/A converters 406 and 515, demodulating means 407, receiving frequency offset estimating means 408, modulating means 517, sending frequency offset estimating means 518 and a central processing unit (CPU) 521.
Also, according to communications apparatus of the second related art, receive signals received via the antenna 401 are frequency-converted via the mixer 402, and a frequency offset estimate FOS is determined via the receiving frequency offset estimating means 408. Reference frequency control, so-called the AFC (Auto Frequency Control) is made by using the CPU 521 to feed back a control value based on the determined frequency offset estimate FOS to the sending frequency offset control means 518 as a frequency offset control value FOC.
While the demodulating means 407 demodulates intermediate-frequency signals frequency-converted by the mixer 402 and outputs upstream control data DTD and downstream control data DCD to the CPU 521, the CPU 521 can control the sending reference frequency by using the downstream control data DCD from the demodulating means 407, besides the AFC processing. In this case, a frequency offset control value FOC is generated by the CPU 521 based on a sending reference frequency command on the downstream control data DCD and fed back to the sending frequency offset control means 518.
According to the conventional communications apparatus equipped with the frequency offset correction feature of the first related art, however, it is a common practice that a VCTCXO (a VCO (voltage controlled oscillator) equipped with a temperature-compensated crystal oscillator (TCXO)) as a reference oscillator is used in terms of power consumption and apparatus cost. This causes degradation in the accuracy of the VCTCXO due to its nonlinearity, temperature characteristics and secular change. As mentioned earlier, According to communications apparatus which controls the sending reference frequency by using downstream control data DCD, it is necessary to feed back the sending reference frequency command to the voltage-controlled oscillator (VCTCXO) 404. In this case, such apparatus cannot control the sending reference frequency with high accuracy due to nonlinearity, temperature characteristics and secular change of the VCTCXO, thus inviting degradation in the accuracy of the sending reference frequency.
Similarly, according to communication apparatus which controls, by using the downstream control data DCD, the sending reference frequency immediately after a new channel is assigned, such as via a handover, it is necessary to feed back the sending reference frequency command to the voltage-controlled oscillator (VCTCXO) 404. In this case, such apparatus cannot control the sending reference frequency with high accuracy due to nonlinearity, temperature characteristics and secular change of the VCTCXO, thus inviting degradation in the accuracy of the sending reference frequency.
According to the conventional communications apparatus equipped with the frequency offset correction feature of the second related art, however, it is a common practice that a temperature-compensated crystal oscillator as a reference oscillator 404 is used in terms of power consumption and apparatus cost. This causes degradation in the accuracy of the TCXO due to its initial deviation, temperature characteristics and secular change. That is, a receiving frequency offset caused by initial deviation, temperature characteristics and secular change inherent to the TCXO invites degradation in the demodulation characteristics in the demodulating means 407.
The invention, in view of the aforementioned circumstances and problems, aims at providing communications apparatus, a frequency control method for communications apparatus, and a recording medium which allow high-accuracy frequency offset correction without degradation in the accuracy of the sending or sending/receiving reference frequency and demodulation characteristics, despite degradation in the accuracy caused by nonlinearity, temperature characteristics and secular change of a voltage-controlled oscillator (VCTCXO) or reference oscillator (TCXO).
To solve the aforementioned problems, communications apparatus according to the first aspect of the invention comprises receiving frequency offset estimating means for estimating a receiving frequency offset based on receive signals, a voltage-controlled oscillator for controlling a local oscillator frequency based on an estimate determined by the receiving frequency offset estimating means, demodulating means for demodulating the receive signals to obtain control data, and sending frequency offset control means for controlling a sending frequency offset based on control data obtained by the demodulating means, wherein a sending reference frequency is controlled by using the voltage-controlled oscillator and the sending frequency offset control means.
According to the second aspect of the invention, communications apparatus performing TDMA communications comprises receiving frequency offset estimating means for estimating a receiving frequency offset based on receive signals, a voltage-controlled oscillator for controlling a local oscillator frequency based on an estimate determined by the receiving frequency offset estimating means, demodulating means for demodulating the receive signals to obtain control data, and sending frequency offset control means for controlling a sending frequency offset by using the local oscillator frequency as a reference, based on downstream control data obtained by the demodulating means, the voltage-controlled oscillator, upon assignment of a new channel, controlling a sending frequency offset based on the downstream control data obtained by the demodulating means to pull the local oscillator frequency, the sending frequency offset control means controlling the sending frequency offset based on the downstream control data obtained by the demodulating means, by using as a reference a local oscillator frequency provided when or immediately before a new channel is assigned, from assignment of a new channel to completion of pulling of the local oscillator frequency.
A frequency control method for communications apparatus according to the third aspect of the invention comprises a receiving frequency offset estimating step for estimating a receiving frequency offset based on receive signals, a frequency control step for controlling a local oscillator frequency based on an estimate determined by the receiving frequency offset estimating step, a demodulating step for demodulating the receive signals to obtain control data, and a sending frequency offset control step for controlling a sending frequency offset based on control data obtained by the demodulating step, wherein a sending reference frequency is controlled by using the frequency control step and the sending frequency offset control step.
According to the fourth aspect of the invention, a frequency control method for communications apparatus performing TDMA communications, comprises a receiving frequency offset estimating step for estimating a receiving frequency offset based on receive signals, a frequency control step for controlling a local oscillator frequency based on an estimate determined by the receiving frequency offset estimating step, a demodulating step for demodulating the receive signals to obtain control data, and a sending frequency offset control step for controlling a sending frequency offset by using the local oscillator frequency as a reference, based on downstream control data obtained by the demodulating step, the frequency control step, upon assignment of a new channel, controlling a sending frequency offset based on the downstream control data obtained by the demodulating step to pull the local oscillator frequency, the sending frequency offset control step controlling the sending frequency offset based on the downstream control data obtained by the demodulating step, by using as a reference a local oscillator frequency provided when or immediately before a new channel is assigned, from assignment of a new channel to completion of pulling of the local oscillator frequency.
A computer-readable recording medium according to the fifth aspect of the invention is a frequency control method for communications apparatus according to the third or fourth aspect of the invention which is stored as a program to be executed by a computer.
According to communications apparatus of the first aspect of the invention, a frequency control method for communications apparatus of the third aspect of the invention, and a recording medium of the fifth aspect of the invention, a receiving frequency offset is estimated, based on receive signals via receiving frequency offset estimating means (a receiving frequency offset estimating step), a local oscillator frequency is controlled, based on an estimate determined by the receiving frequency offset estimating means (receiving frequency offset estimating step) via a voltage-controlled oscillator (a frequency control step), receive signals are demodulated to obtain downstream control data via demodulating means (a demodulating step), and a sending frequency offset is controlled via sending frequency offset control means (a sending frequency offset control step) based on downstream control data obtained by the demodulating means (demodulating step), to control a sending reference frequency by using the voltage-controlled oscillator (frequency control step) and the sending frequency offset control means (sending frequency offset control step).
According to communications apparatus of the first aspect of the invention, a frequency control method for communications apparatus of the third aspect of the invention, and a recording medium of the fifth aspect of the invention, control of a reference frequency (local oscillator frequency) or AFC is made by feeding back a frequency offset estimate to the voltage-controlled oscillator, and the frequency offset between sending and receiving frequencies is corrected by feeding back a frequency offset control value which is based on for example a sending reference frequency command on control data to sending frequency offset control means, to control a sending reference frequency by using both a voltage-controlled oscillator (a frequency control step) and sending frequency offset control means (a sending frequency offset control step). This allows high-accuracy frequency offset correction without degradation in the accuracy of the sending reference frequency and demodulation characteristics, despite degradation in the accuracy caused by nonlinearity, temperature characteristics and secular change of a voltage-controlled oscillator (VCTCXO) or reference oscillator (TCXO).
According to communications apparatus of the second aspect of the invention, a frequency control method for communications apparatus of the fourth aspect of the invention, and a recording medium of the fifth aspect of the invention, a receiving frequency offset is estimated, based on receive signals via receiving frequency offset estimating means (a receiving frequency offset estimating step), a local oscillator frequency is controlled, based on an estimate determined by the receiving frequency offset estimating means (receiving frequency offset estimating step) via a voltage-controlled oscillator (a frequency control step), downstream control data is obtained by demodulating means (a demodulating step), and a sending frequency offset is controlled via sending frequency offset control means (a sending frequency offset control step) based on downstream control data obtained by the demodulating means (demodulating step) by using a local oscillator frequency as a reference. When a new channel is assigned, a sending frequency offset is controlled, based on downstream control data obtained by the demodulating means (demodulating step) to pull the local oscillator frequency via a voltage-controlled oscillator (a frequency control step), and a sending frequency offset is controlled, based on downstream control data obtained by the demodulating means (demodulating step), via the sending frequency offset control means (sending frequency offset control step) by using as a reference the local oscillator frequency provided when or immediately before a new channel is assigned, from assignment of a new channel to completion of pulling of the local oscillator frequency.
For example, when a new channel is assigned via for example a handover command, a new reference frequency (local oscillator frequency) via AFC is pulled by feeding back a frequency offset control value which is based on a receiving reference frequency command on downstream control data to a voltage-controlled oscillator to control a sending frequency offset. From assignment of a new channel to completion of pulling of the reference frequency, a sending frequency offset is controlled by (feeding back a frequency offset control value) which is based on a receiving reference frequency command on downstream control data to sending frequency offset control means, by using as a reference the reference frequency provided when or immediately before a new channel is assigned, not a reference frequency provided in the course of pulling the reference frequency. This allows high-accuracy frequency offset correction without degradation in the accuracy of the sending/receiving reference frequency and demodulation characteristics immediately after a new channel is assigned, despite degradation in the accuracy caused by nonlinearity, temperature characteristics and secular change of a voltage-controlled oscillator (VCTCXO) or reference oscillator (TCXO).